1. Field of the Invention
The present invention relates generally to injection molding apparatuses, for manufacturing metal molded articles, which comprise an upper unit including an ingot entry and an ingot heating chamber, and a lower unit including a crushing chamber provided with cutters and an injecting machine provided with a screw shaft.
More particularly, the present invention relates to an improved injection molding apparatus which, with a simple construction, can reliably absorb undesirable thermal expansion of the lower unit and mechanical shocks and vibrations caused in the lower unit by the injecting action of the injecting machine.
The present invention also relates to an improved injection molding apparatus which, with a simple construction, permits easy access to the upper and lower units for facilitated maintenance operations of the apparatus.
The present invention also relates to an improved mechanism for sealing an ingot heating chamber in an injection molding apparatus, which comprises an upper door for openably closing the top of the heating chamber and lower door for openably closing the bottom of the heating chamber and which can reliably seal the heating chamber in a predetermined atmospheric condition by means of the upper and lower doors without requiring a large operating space for the lower door and without the lower door being damaged by a heated ingot.
2. Description of the Related Art
In Japanese Patent Laid-open Publication No. HEI 5-285625, the assignee of the present invention proposes an injection molding apparatus for manufacturing metal molded articles, which is designed to increase productivity by heating and slurring an ingot in successive operations as will be outlined below with reference to FIG. 16.
FIG. 16 is a vertical sectional view schematically showing the proposed injection molding apparatus 100, which generally comprises a screw-type injecting machine 101 including a screw shaft 111 axially movable within a machine cylinder and having a spiral groove along a predetermined length thereof, and a material feeder section 102. The material feeder section 102 includes, in the top-to-bottom direction of the figure, an ingot entry 103, ingot heating chamber 104 provided with an inductive heater, and crushing chamber 107 having rotary cutters 106. The crushing chamber 107 is connected in communication with the heating chamber 104 via a heat-retaining chamber 105. The interior of the entire material feeder section 102 is maintained in a vacuum or inert gas atmosphere, and the above-mentioned chambers 103, 104 and 105 are partitioned off by sliding shutters 108 and 109.
In the proposed injection molding apparatus 100, an ingot 110 fed via the ingot entry 103 is heated in the heating chamber 104 into a half-molten condition and passed through the chamber 105 to the crushing chamber 107 to be crushed by the rotary cutters 106. Then, the crushed ingot pieces are introduced into the injecting machine 101, where they are agitated and kneaded into slurry by rotation of the screw shaft 111 and temporarily accumulated in the tip end portion of the cylinder as a final slurried material to be molded. Once a predetermined amount of the slurried material has been accumulated, it is directly or indirectly injected through a nozzle into a cavity 113 of a metal mold 112 by injecting action of the screw shaft 111. Because the ingot 110 is heated in the heating chamber 104, passed through the heat-retaining chamber 105 and then cut into pieces by the cutters 106, the necessary injecting operations of the apparatus 100 can be carried out in succession, which thus promotes increased productivity of the apparatus 100.
In the injection molding apparatus 100, the injecting machine 101, crushing chamber 107 and heat-retaining chamber 105 together constitute a lower unit of the molding apparatus 100, while the heating chamber 104 and ingot entry 103 together constitute an upper unit of the apparatus 100. The lower unit is mounted on a support base 114, and the upper unit is fixedly connected to the lower unit via bolts and other forms of complicated joints. In the lower unit of the apparatus 100, the material supplied from the upper unit is crushed while being retained at a predetermined high temperature and then fed into the injecting machine 101, where it is also retained at the high temperature, accumulated, again heated if necessary, and finally forced out to the mold 112.
Generally, in prior art injection molding apparatuses such as the above-mentioned apparatus 100, the outer atmospheric temperature around the upper unit including the heating chamber is compulsorily maintained cold to prevent overheating by the heating chamber, but the outer atmospheric temperature around the lower unit is left warm for the above-mentioned heat-retaining purposes. Consequently, the lower unit tends to thermally expand upward, so that there would arise a substantial mechanical interference in the connection between the upper and lower units. Additionally, the injecting action of the injecting machine in the lower unit involves considerable mechanical shocks and vibrations, which are transmitted to the upper unit by way of the various components of the lower unit. Such shocks and vibrations transmitted would sometimes damage the ingot in the entry of the upper unit.
Further, in the prior art injection molding apparatuses, the feeding of the ingot to the entry, heating chamber, crushing chamber and injecting machine is via a sealed continuous passage within the apparatus; while, the heating and crushing of the ingot and slurring and injecting of the crushed ingot within the injecting machine are executed in an inert gas atmosphere in order to prevent unwanted oxidation of the ingot. The inductive heater in the heating chamber, the cutters in the crushing chamber, the nozzle and screw shaft in the injecting machine, etc. would fail or wear due to their long-time use, and thus these components need to undergo maintenance operations such as inspection, repair, part replacement, etc. from time to time or on a periodical basis.
However, for maintenance operations of the prior art molding apparatuses, at least the upper and lower units must be disconnected from each other by releasing the bolts and other joints and then must be separated enough for easy access thereto by a human operator. Therefore, the maintenance operations were very difficult and time-consuming. Besides, the prior art molding apparatuses required a large space for the separation of the upper and lower units.
Further, in the prior art injection molding apparatuses, the heating chamber must be hermetically sealed to reliably remain in a vacuum or inert gas atmosphere. One approach is disclosed in Japanese Patent Laid-open publication No. HEI 5-285626, where sliding shutters or doors are provided in the upper and lower portions of the heating chamber so as to seal between the ingot entry, heating chamber and crushing chamber. However, it was difficult to attain reliable sealing by the lower door disclosed in the 5-185626 publication. In addition, even if the reliable sealing is attained at all, a relatively large space would be required for sliding the doors to open. In particular, because the lower door is slid with the heated ingot placed thereon, it would easily wear and get damaged by the heated ingot as it slides relative to the ingot for opening or closing the heating chamber.